1. Field of the Invention
This invention pertains generally to rotary kinetic energy storage and retrieval mechanisms, and more particularly to flywheel batteries for converting electric power and storing it as kinetic energy, and regenerating electric power on demand.
Specifically it sets forth flywheel assemblies having a vertical spin axis supported axially by passive magnetic bearings, stabilized radially by ceramic ball bearings, cooperative with an integral regenerative motor controlled by power interface electronics, to provide practical long-duration electrical energy storage and regeneration, with minimal energy losses.
2. Description of the Related Art
Over the past 40 years, flywheel batteries have been set forth in the prior art, having various forms and combinations, intended to convert electric power to kinetic energy stored in a spinning flywheel, and generate electric power from its rotary inertia. Most of these flywheel storage devices provide only short duration power due to their high continuous losses. They require periodic maintenance, so they are usually housed in accessible locations. These locations are generally not consistent with flywheel safety. A flywheel that does not require maintenance can be housed in a relatively inaccessible location that can safely absorb the stored flywheel energy if it should ever explosively disintegrate.
A safe, cost-competitive, minimal-loss, zero-maintenance flywheel battery for providing long duration power and having a long service life, would provide significant benefits over high-power-loss flywheel storage that provides only short duration power, chemical battery storage, and fuel-burning generators, or combinations of chemical battery and flywheel storage to start fuel-burning generators used in stationary sites.
The present invention is intended to provide lower-cost reliable long-term safe zero-maintenance minimal-loss power storage and regeneration. It also is intended to facilitate practical on-site distributed solar and wind power installations. Parallel connection with like flywheel batteries (facilitated by its current control) enables flexible power and energy scaling capacity, to meet needs of various power installations and power grid load leveling.
For over 160 years, inventors have been working on many passive magnetic levitation configurations, to circumvent instability considerations described by Eamshaw, Gauss, and Maxwell. Flywheel rotor bearings affect configurations and element combinations of the entire flywheel battery system. My present invention does not need servo sensors, electronics, nor electromagnets, for its rotor bearings. This affords synergistic opportunities to use less parts in its power interface electronics and regenerative motor as well. New configurations, combinations, and improvements enabled by magnets that support the flywheel rotor weight, and ceramic ball bearings that center the rotor but do not sustain radial loads, are explained and illustrated herein.
Magnetic bearings without electronic servo loops are described in U.S. Pat. Nos. 5,495,221 and 5,783,885 plus 5,847,480 and 5,861,690 plus 5,883,499 and 6,111,332 by Post. They teach stable axial lift-off and/or radial centering, from repulsion forces caused by relative motion, between superconductor magnets (high-current conductors that produce magnetic fields opposing changing magnetic fields and so cause forces that levitate and center a spinning juxtaposed Halbach magnet array). Said patents teach mechanical bearings for rotor support at speeds lower than needed to achieve requisite magnetic lift-off or centering forces; and means for superconductor magnets to achieve repelling forces at ambient temperatures, plus means to automatically disengage mechanical bearings when requisite rotor spin speed is reached.
Conversely, my distinctly different present invention describes a flywheel battery that includes new power electronics, different rotor bearings which incur minimal power losses, a regenerative motor magnet array whose spinning magnetic field is confined to motor stator windings which minimize eddy current losses therein, and mechanical backup bearings to enhance safety and minimize damage in the event that the normal operation rotor bearings were to fail.
High rotor speeds are needed, to achieve compact flywheels with high energy/weight ratios. This requires a vacuum enclosure, to avoid excessive power drain due to air drag. Vacuum loss in prior art flywheel enclosures, due to flywheel assembly parts outgassing, may necessitate an integral vacuum pump, or costly maintenance, to keep air drag loss at acceptably low levels. Prior art flywheel assemblies that need periodic maintenance (mostly to lubricate and some times to replace mechanical bearings) would also need to be located where they are accessible. That usually precludes their installation in a site that can safely absorb the energy released if the flywheel rotor disintegrates while spinning at high speed.
Viscous friction in mechanical bearings that need lubrication can cause considerable drag torque at high spin speeds, and vacuum loss due to lubricant evaporation. Mechanical bearings of some prior art would incur serious heating and wear, running in vacuum at sustained high speed. Also, very high operating temperatures of critical bearing parts have been caused by heat generated from bearing losses, compounded by low heat transfer, further compounded by bearing lubrication loss accelerated by lubricant boil-off in vacuum. Ball bearings and roller bearings subjected to radial loads cause vibration due to ball passing events (a problem explained herein, with unique and distinct means to mitigate it). Prior art ball bearing applications have resulted in early bearing wear, their subsequent deterioration, and high failure rates. Prior art flywheel teachings do not include design considerations to mitigate precession torque due to Earth rotation (which tends to tilt the rotor assembly and therefore adds to rotor bearing radial loads). The prior art includes many combinations of magnetic and mechanical bearings, with distinct differences from my present invention, and does not describe the design considerations and system integration presented herein, nor means to improve ball bearing service life described herein.
Conversely, the present invention sets forth new configurations of ceramic ball bearings with lubricant coating, and thus almost no viscous drag nor vacuum enclosure contamination due to oil or grease lubricant evaporation. Said ceramic ball bearings, and their combination as set forth herein with cooperative flywheel assembly parts, have angular contact resulting from precision axial preload, incur minimum steady-state radial bearing loads, and thus mitigate ball pass vibration. These improvements are mainly intended to increase ball bearing service life.
Rechargeable chemical batteries are commonly used for storing on-site electric power. All types require frequent maintenance, may fail without warning, and deteriorate over time. Their lifetimes are usually limited to less than ten years—far shorter if subjected to repeated frequent deep charge and discharge cycles or not promptly recharged after supplying power. Most have toxic waste disposal problems. These battery drawbacks have been a major obstacle to on-site solar and wind power installations, because power storage, especially for off-grid installations, is subjected to daily charge and discharge cycles. Wind power is sporadic, and imposes additional power storage charge and discharge demands. To provide power on demand, such installations require power storage that is subjected to daily and highly variable charge and discharge cycles.
Accordingly, the present invention is intended to provide a reliable, safe, zero-maintenance, minimal-loss, and cost-competitive power storage and regeneration option, providing far longer service life that is not shortened by a practically unlimited number of charge and discharge cycles.
U.S. Pat. No. 6,630,761 for “Combination Mechanical and Magnet Support for a Flywheel Power Supply” and U.S. Pat. No. 6,710,489 for “Axially Free Flywheel System” by Gabrys, teach combination magnetic and mechanical flywheel rotor bearings, that have distinct and substantial differences from the rotor bearings of my present invention. These prior patents describe ball bearings within a very different configuration compared to applicant's present invention, in that they teach a different configuration of axial support magnets, and teach radial support by ball bearings whose inner races spin with a rotor shaft (whereas the present invention sets forth two ball bearings whose outer races spin with the flywheel rotor). Said prior patents do not teach spring means to apply a consistent ball bearing inner race lift force, which provides both a stable rotor lift force plus a consistent axial preload for the two ball bearings spaced a maximum practical axial distance from each other. Said prior patents do not address means to mitigate radial loads to ball bearings caused by Earth rotation precession torque which acts on a spinning flywheel rotor assembly. Said prior patents also do not teach system configurations and integration details with a regenerative motor and power electronics, as set forth in applicant's present invention.
Configurations and details of applicant's present invention, and their differences from said patents, are described and illustrated herein.
U.S. Pat. No. 6,897,587 by McMullen and entitled “Energy Storage Flywheel With Minimum Power Magnetic Bearings And Motor/Generator”, the contents which are incorporated herein by reference, teaches active axial and radial magnetic bearings to support the flywheel rotor, which include mechanical backup rotor bearings, and materials that minimize cost of parts, to achieve lower cost flywheel systems. Conversely, applicant's present invention sets forth repelling magnet axial support and ball bearing radial stabilization. This prior art patent describes flywheel system embodiments and component configurations with distinct and substantial differences from applicant's present invention, and does not teach combinations of electronics, magnetics and mechanical elements, integrated as set forth in applicant's present invention. Said patent also does not teach means to mitigate problems from level shifting and from precession torque due to Earth rotation. Whereas applicant sets forth herein a flywheel assembly in a vacuum enclosure supported by self-leveling means, a feature described herein to facilitate installation, minimize idling losses, and accommodate possible ground shift over the flywheel service life.
The list of prior flywheel and related element patents cited here represents a very small fraction of many patents, which describe many possible diverse flywheel configurations. Other exemplary patents for flywheels and for other apparatus which may or may not be related but which provide illustration from which the teachings are incorporated herein by reference, include: U.S. Pat. No. 2,340,781 by Wagner; U.S. Pat. No. 2,651,550 by Sharp; U.S. Pat. No. 2,869,934 and U.S. Pat. No. 2,869,935 by Milligan et al; U.S. Pat. No. 3,107,310 by Carriere et al; U.S. Pat. No. 3,107,948 by Joseph Lovegrove; U.S. Pat. No. 3,114,582 by Milligan; U.S. Pat. No. 3,124,396 by Barager; U.S. Pat. No. 3,143,704 by Wright; U.S. Pat. No. 3,157,053 by Hall; U.S. Pat. No. 3,221,389 by Cowell; U.S. Pat. No. 3,233,950 and U.S. Pat. No. 3,326,610 by Baermann; U.S. Pat. No. 3,584,276 by Ringland et al; U.S. Pat. No. 3,597,023 by Baermann; U.S. Pat. No. 3,657,676 by Milligan; U.S. Pat. No. 3,696,277 by Liska et al; U.S. Pat. No. 3,731,984 by Habermann; U.S. Pat. No. 3,761,148 by Grosbard; U.S. Pat. No. 3,791,704 by Perper; U.S. Pat. No. 3,794,391 by Grosbard; U.S. Pat. No. 3,807,813 by Milligan; U.S. Pat. No. 3,810,683 by Keever et al; U.S. Pat. No. 3,811,740 by Sacerdoti et al; U.S. Pat. No. 3,856,200 by Lieb; U.S. Pat. No. 3,860,300 by Lyman; U.S. Pat. No. 3,899,223 by Baermann; U.S. Pat. No. 4,080,012 by Boden et al; U.S. Pat. No. 4,127,799 by Nakamura et al; U.S. Pat. No. 4,295,083 by Leenhouts; U.S. Pat. No. 4,358,723 by Scholl et al; U.S. Pat. No. 4,371,801 by Richter; U.S. Pat. No. 4,390,865 by Lauro; U.S. Pat. No. 4,444,444 by Benedetti et al; U.S. Pat. No. 4,483,570 by Inoue; U.S. Pat. No. 4,511,190 by Caye et al; U.S. Pat. No. 4,563,046 by Shimamoto; U.S. Pat. No. 4,668,885 by Scheller; U.S. Pat. No. 4,700,094 by Downer et al; U.S. Pat. No. 4,723,735 by Eisenhaure et al; U.S. Pat. No. 4,732,353 by Studer; U.S. Pat. No. 4,785,212 and U.S. Pat. No. 4,961,352 by Downer et al; U.S. Pat. No. 5,126,317 by Agarwala; U.S. Pat. No. 5,159,219 by Chu et al; U.S. Pat. No. 5,202,598 by Katsumata; U.S. Pat. No. 5,204,569 by Hino et al; U.S. Pat. No. 5,214,981 by Weinberger et al; U.S. Pat. No. 5,220,232 by Rigney II et al; U.S. Pat. No. 5,314,868 by Takahata et al; U.S. Pat. No. 5,386,166 by Reimer et al; U.S. Pat. No. 5,392,176 by Anderson; U.S. Pat. No. 5,398,571 by Lewis; U.S. Pat. No. 5,419,212 by Smith; U.S. Pat. No. 5,436,516 by Yamazaki et al; U.S. Pat. No. 5,441,222 by Rosen; U.S. Pat. No. 5,514,923 by Gossler et al; U.S. Pat. No. 5,521,448 by Tecza et al; U.S. Pat. No. 5,540,116 by Hull et al; U.S. Pat. No. 5,614,777 by Bitterly et al; U.S. Pat. No. 5,675,201 by Komura et al; U.S. Pat. No. 5,679,992 by Miyamoto et al; U.S. Pat. No. 5,681,012 by Rosmann et al; U.S. Pat. No. 5,703,423 by Fukao et al; U.S. Pat. No. 5,708,312 by Rosen et al; U.S. Pat. No. 5,722,303 by Hull et al; U.S. Pat. No. 5,754,425 by Murakami; U.S. Pat. No. 5,831,362 by Chu et al; U.S. Pat. No. 5,880,544 by Ikeda et al; U.S. Pat. No. 5,969,446 by Eisenhaure et al; U.S. Pat. No. 5,977,677 by Henry et al; U.S. Pat. No. 6,019,319 by Falbel; U.S. Pat. No. 6,121,704 by Fukuyama et al; U.S. Pat. No. 6,130,831 by Matsunaga; U.S. Pat. No. 6,166,472 by Pinkerton et al; U.S. Pat. No. 6,182,531 by Gallagher et al; U.S. Pat. No. 6,231,011 by Chu et al; U.S. Pat. No. 6,236,127 by Bornemann; U.S. Pat. No. 6,262,505 by Hockney et al; U.S. Pat. No. 6,288,670 by Villani et al; U.S. Pat. No. 6,388,347 by Blake et al; U.S. Pat. No. 6,420,810 by Jeong; U.S. Pat. No. 6,486,627 and U.S. Pat. No. 6,570,286 by Gabrys; U.S. Pat. No. 6,603,230 by Abel; U.S. Pat. No. 6,664,880 by Post; U.S. Pat. No. 6,700,259 by Lin et al; U.S. Pat. No. 6,703,735 by Gabrys; U.S. Pat. No. 6,727,616 by Gabrys et al; U.S. Pat. No. 6,727,617 by McMullen et al; U.S. Pat. No. 6,750,588 by Gabrys; U.S. Pat. No. 6,770,995 by Foshage; U.S. Pat. No. 6,794,776 and U.S. Pat. No. 6,798,092 and U.S. Pat. No. 6,806,605 by Gabrys; U.S. Pat. No. 6,825,588 by Gabrys et al; U.S. Pat. No. 6,867,520 by Jennings; U.S. Pat. No. 7,053,589 by Gabrys et al; U.S. Pat. No. 7,119,520 by Wingett et al; U.S. Pat. No. 7,263,912 by Gabrys et al; U.S. Pat. No. 7,276,828 by Yeh et al; and 2003/0052558 by Brackett et al.
None of these configurations, nor other prior art known to applicant, includes the minimal-loss features of the regenerative motor and power interface electronics combined with the flywheel rotor bearings described herein, and other features described in applicant's U.S. Pat. Nos. 6,566,775 and 6,794,777. Additional patents by the present inventor, the teachings which are also incorporated herein by reference, include U.S. Pat. Nos. 4,085,355 and 4,520,300.
The present invention is intended to provide a reliable, safe, zero-maintenance, minimal-loss, and cost-competitive power storage and regeneration option, providing far longer power delivery times enabled mainly by minimal idling losses, compared to other flywheel batteries, and far longer service life that is not shortened by a practically unlimited number of charge and discharge cycles, compared to chemical batteries. Some of the main principles described in my prior patents are included in my present invention, with distinct differences and combinations, facilitated mainly by the new flywheel rotor bearing configuration set forth herein, improved electronics, and less parts needed to provide a substantially lower cost flywheel battery having comparable performance.
Applicant's present invention sets forth new flywheel battery elements, configurations, and combinations, to reduce parts and labor cost of the flywheel systems described in applicant's U.S. Pat. No. 6,794,777 for a “Robust Minimal-Loss Flywheel System”. Said patent teaches a flywheel having contactless servo-stabilized magnetic bearings. It also teaches means for achieving virtually zero “idling loss” (a flywheel battery property comparable to chemical battery “self discharge”) while its magnetically levitated rotor spins at high speeds, with configurations that avoid magnetic cycling of magnetic materials, and that block and buck eddy currents in stator windings. Said patent also teaches motor/generator means for high electromechanical power conversion efficiencies and nearly zero power loss while coasting at all speeds, and systems that can have virtually unlimited service life without need for maintenance. It also teaches power interface electronics, which exchange current with its DC (direct current) power bus and its motor/generator. It teaches magnetic levitation means that require virtually zero steady-state power. Its many attributes are very useful, but achieving them is difficult and requires very exacting conditions.
Conversely, applicant's present invention sets forth a flywheel battery with less difficult requirements and fewer parts, compared to elements and combinations taught in my U.S. Pat. No. 6,794,777. The present invention will reduce much flywheel battery cost and weight. It has fail-safe passive magnetic and ball bearings, with sliding surface backup. Its rotor bearings do not require position and rate sensors, feedback control loops, electromagnets, and power for them. However, it needs critical rotor balance and vibration damping means, to prevent damage to its ceramic ball bearings by rotor vibration, major earthquakes, and extreme shaking. Flywheel assembly ball bearing position, to minimize ball bearing radial loads due to Earth rotation, is analyzed and described in detail herein. Electronics of my present invention, which serve as interface between the motor stator windings, rotor angle sensors, and a DC power bus, include distinct differences, compared to electronics described in U.S. Pat. No. 6,794,777. Moreover, electronics of my present invention do not need to implement startup and turn-off algorithms for active magnetic bearings. New features are explained by way of drawings, detailed element and system interaction explanations, functional circuit schematics, current and voltage waveforms, and manufacturing process descriptions herein.
The flywheel assembly described in applicant's U.S. Pat. No. 6,794,777 contains 10 Hall-effect position sensors and 10 rate sensor coils, to provide magnetic bearing servo feedback signals. They must accurately sense magnetic fields responsive to axial and radial rotor position, with tolerances under a few gauss. So they must be shielded from nearby magnetic fields in a 10-kilogauss range. Servo PCBs (Printed Circuit Boards) responsive to said sensors must each be located on corresponding top and bottom flywheel assembly decks, very close to their respective sensor. An axial servo PCB, mounted to the top deck of my prior flywheel assembly prototype, needs signals from sensors at the top and bottom; so signal conductors between sensors at the bottom of the assembly to said PCB must be shielded from electromagnetic interference.
Additionally, ground loops (signal interference caused by small fractions of high electromagnet actuator currents in signal grounds) are troublesome. Moreover, although only minimal power for the prototype flywheel rotor's magnetic bearing servos will be needed during steady-state operation, peak power demand for said servos at startup or while limit-cycling can exceed 1000 watts. Radial and axial control must be simultaneously activated, because axial control alone is susceptible to rotor tilt instability; as predicted by analysis and witnessed during tests. And axial force needed to pull the prototype's 60-pound rotor to its optimum operating height, from a top starting position, is a few hundred pounds; requiring a large bottom axial electromagnet and very sturdy frame to support such high forces. A large top axial electromagnet, having large gaps in its iron poles, is also needed. As was predicted by SPICE analyses of very accurate and detailed servo loops, and demonstrated by applicant's prototype, magnetic bearing servo limit-cycling will occur unless many exacting conditions are met. Also, flywheel assembly tasks are relatively complex for said prior flywheel battery, and unless crucial precautions are heeded, can be hazardous to assemblers, working with magnetic forces up to a few hundred pounds between parts, caused by permanent magnets in the assembly. Assembly procedures are very difficult, involving such high force requirements and high stray fields, combined with very small, sensitive and delicate sensors. Therefore, labor and tooling cost is also considerably higher, for flywheel batteries taught in applicant's prior patents.
My prior patents teach a flywheel rotor supported during steady-state operation by magnetic means affixed to a top deck, whereas the flywheel rotor of my present invention is supported entirely by a bottom deck. Moreover, the maximum normal support force on the bottom deck of the present invention is only a small amount more than the rotor weight. This permits a substantially lighter flywheel battery having a larger rotor assembly.
Accordingly, a primary objective of the present invention is to provide a minimal-loss rotor bearing, which does not require the magnetic bearing servos taught in U.S. Pat. No. 6,794,777. My present invention has 8 connections, in its flywheel assembly illustrated in FIG. 1, whereas axial and radial position and rate sensors, PCBs, power transistors, and electromagnet coils in the flywheel assembly of my prior art patent needs over 100 connections. The total number of parts needed by the new flywheel battery system is far less. The present invention also obviates assembly and setup difficulties; and thereby is intended to achieve comparable performance with considerably less than half the labor cost for the flywheel assembly, and about half the total labor and parts cost for each flywheel battery system. The magnetic levitation configuration of my present invention is intended to achieve virtually zero hysteresis and eddy current losses as well, because no iron, no high-permeability steel, and no magnets are subjected to magnetic flux cycling, nor to substantial magnetic flux variation, due to rotor spin. So performance should be comparable to the flywheel batteries described in my prior patents.
General objectives of this present invention are to provide lower cost flywheel batteries, for stationary installations, affording very long and reliable service life with zero maintenance, and additionally incurring far lower energy losses than other prior art flywheel power storage devices.
A specific objective of the present invention is to provide combination magnetic and ceramic ball bearings described herein, and improvements facilitated thereby, to reduce flywheel battery cost and weight, without sacrificing high electromechanical power conversion efficiency, safety, durability, reliability, and minimal idling losses, as design trade-offs.
Axial preload means, for extending ball bearing service life, by preventing ball skips, skids, bounces, jumps, and ball pass vibration, which also augment rotor lift force, are a key part of this objective. The axial preload is also intended to precisely center the rotor with sufficient radial compliance to prevent rotor unbalance pounding the ball bearings at high spin speeds.
Flywheel assembly relative height and diameter considerations, which mitigate radial loads on ball bearings caused by Earth rotation precession torque, is an important related objective.
Another specific objective of the present invention is to provide self-leveling means for the flywheel assembly in its vacuum enclosure, to reduce installation labor cost and to prevent early ball bearing failure from radial loads caused by land shifting after flywheel battery installation.
Broad objectives of the present invention include a flywheel electric power storage system, and the elements to implement it, to provide practical cost-effective minimal-loss long-life DC (direct current) power. The flywheel has a vertical spin axis. It includes a flywheel assembly having new rotor bearings to provide axial rotor support by magnetic repulsion, with rotor centering stabilized by ceramic ball bearings having axial preload springs that prevent vibration and augment rotor support. Moreover, it has a regenerative permanent-magnet motor controlled by cooperative electronics, the motor integrated within its flywheel assembly, inside a vacuum enclosure having self-leveling means, connected by power and signal conductors to improved power interface electronics. The electronics includes new circuit elements, to produce high-frequency pulse-width-modulation on/off power switching control from analog signals, with over-voltage protection and turn-on delays to prevent unintended current and voltage that could otherwise damage power semiconductors.
In addition to the aforementioned patents and published applications, Webster's New Universal Unabridged Dictionary, Second Edition copyright 1983, is incorporated herein by reference in entirety for the definitions of words and terms used herein.